Multifilar flexible rotary shaft and medical instruments incorporating the same

ABSTRACT

A multifilar flexible rotary shaft includes a plurality of individual filaments which are not wound around each other or around a central core, a loose ensemble of filaments. The input ends of each filament are coupled to each other and the output ends of each filament are coupled to each other. Preferably all of the filaments are identical. A loose ensemble of N filaments can transmit N times the torque of a single filament, and will have N times the torsional stiffness of a single filament, while retaining the minimum radius of operation of a single filament. Since a loose ensemble of filaments does not have any appreciable contact forces among the filaments (because they are not forcibly twisted together), there is no appreciable internal friction or hysteresis. In order to appreciably eliminate all the hysteresis in such an ensemble of filaments, the filaments should be no more than loosely twisted together, if at all. The only reason for loosely twisting the wires together is to allow the ensemble to be easily handled and to insure that the individual wire filaments follow the same general curved path from one end to the other. Several practical applications of the invention are also disclosed.

This application is a continuation of application Ser. No. 09/418,769,filed Oct. 15, 1999 now U.S. Pat. No. 6,404,727. This application isrelated to co-owned application Ser. No. 09/369,724 filed Aug. 6, 1999,entitled: “Polypectomy Snare Instrument” the complete disclosure ofwhich is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to flexible rotary shafts. More particularly, theinvention relates to a multifilar flexible rotary shaft having reducedhysteresis, increased torque transmission, and low internal friction.The shaft of the invention is particularly useful as a component ofminimally invasive surgical instruments which must traverse a tortuouspath.

2. State of the Art

Flexible rotary shafts are used in many applications in order totransmit a torque through a curved path. Generally, a flexible rotaryshaft has an input end which is coupled to a source of rotational energy(e.g. a motor) and an output end which is coupled to something to berotated. In some applications, a single, monofilar, wire is used. Amonofilar flexible rotary shaft must have sufficient yield strength toresist permanent distortion when bent around a specified radius ofcurvature, or “radius of operation”. Indeed, when designing a monofilarflexible rotary shaft, the designer must first determine the radius ofoperation, i.e. the smallest radius the shaft will be expected totraverse. The maximum wire diameter for the radius of operation can bedetermined solely on the yield strength and modulus of elasticity of thewire used. A wire of a given material having a diameter larger than thismaximum would be permanently deformed if bent around the radius ofoperation.

Once the maximum diameter of a monofilar flexible rotary shaft isdetermined for a particular radius of operation, the designer mustdetermine whether the wire has strength and torsional stiffness for aparticular application. Monofilar flexible rotary shafts are notoriouslyinadequate for transmitting a relatively large torque through relativelysmall radius of operation.

Traditionally, multifilar flexible rotary shafts have been employed fortransmitting a relatively large torque through relatively small radiusof operation. Prior Art FIGS. 1 and 2 illustrate a simple multifilarshaft. A typical multifilar flexible shaft 10 consists of a plurality ofwire filaments, e.g. 11, 12, 14, 16, 18, 20, wound, typically about acenter filament, e.g. 22, in a helical organization. Though not shown inprior art FIGS. 1 and 2, often several layers of filaments are wound inalternating opposite directions. While these constructions overcome thedeficiency of monofilar flexible rotary shafts, they nevertheless havetheir own disadvantages. The most notable disadvantage of multifilarflexible rotary shafts is increased hysteresis which results frominternal friction among the filaments. Hysteresis is the term generallyused to describe the difference in the behavior of the input and outputends of a flexible rotary shaft. In its simplest form, hysteresis refersto a time delay between the application of torque at the input end andthe resulting rotation of the output end. Hysteresis also refers toother, erratic, behavior of the output end which is not identical to thebehavior at the input end.

Internal friction and hysteresis in multifilar flexible rotary shaftsresults from the manner in which they are constructed. Specifically, theindividual wires are deformed during the winding process so that theybear against one another in such a way that the assembly “holds itselftogether.” That is, if one disassembles such a flexible shaft, one willfind that the individual wires are deformed into a helical shape, andeach layer grips the next inner layer with a certain amount ofcompression. This type of construction is known as a “pre-formed” cable,because the individual wires are formed into helical shapes during thestranding process. If such cables were not made in this way, they wouldbe very difficult to handle as a subassembly because they would springapart when the ends were cut. In fact, some flexible shafts do springapart to some extent when cut, but in all known multifilar flexibleshafts the individual wires are permanently deformed into a helicalshape. Because of this, there are considerable compressive contactforces among the wires, resulting in friction between the wires when theshaft is rotated while traversing a curved path. This internalwire-to-wire friction results in energy absorption in the flexibleshaft, so that energy delivered to the output end is less than theenergy applied to the input end.

It is known that the filaments of a flexible shaft generate internalfriction which increases as its radius of operation decreases. Further,for a given radius of operation, the more flexible the shaft, the lowerwill be the amount of internal friction. The torque needed to overcomethe resistance due to this internal friction is called the “torque torotate.” As such, the torque-to-rotate value of a given shaft isnormally specified for a specific radius of operation. It follows,therefore, that the more flexible the shaft, i.e., the higher thebending flexibility, the lower will be the torque to rotate for a givenradius of operation.

Torsional stiffness and torsional deflection denote inverse parametersof a flexible shaft. Torsional stiffness specifies a measure of theresistance of the shaft to an applied torque, i.e., a twisting or atorsional force, about its rotational axis. Torsional deflectiondesignates the degree of twist per unit length that a flexible shaftwill experience due to an applied torque. The torsional deflection isusually expressed in degrees per foot per pound-inch (deg/ft/lb-in); itsinverse, torsional stiffness, is expressed in units of lb-in/ft/deg.

Therefore, when choosing a flexible shaft, the length of the smallestradius of operation and the magnitude of the input torque are importantfactors in determining the bending flexibility of the shaft. Thefollowing conditions should be met when selecting a flexible shaft:first, the shaft must have sufficient bending flexibility so as not tobe damaged when flexed into its smallest radius of operation; second,the shaft must have sufficient flexibility so that the torque-to-rotatevalue at the smallest radius of operation is at least less than theinput torque, i.e., the output torque of the driver element; and third,the shaft must have sufficient torsional stiffness to accuratelytransmit rotary motion with a minimum of torsional deflection.

Most designers believe that the mechanism of torque transmission along amultifilar flexible shaft is by means of tensile (and compressive)stresses in the individual wires. In fact, for existing multifilarflexible shafts transmitting large torques this is essentially true.When subjected to high torques, such multifilar assemblies react by somelayers expanding and some contracting (depending upon the direction oftwist). If the inner are expanding layers, they are resisted by outercontracting layers, so the torque is resolved into tensile stresses inthe contracting layers and compressive stresses in the expanding layers.This reaction to torque thus results in contact forces between thelayers of wire, and these contact forces result in friction. As aresult, there is noticeable lost rotary motion at the output end of theflexible shaft when the input torque is alternated from one direction tothe other, as in the case of a shaft used to steer a medical device orto transmit a rotary position signal. When the input of the shaft istwisted in one direction from its static condition, a certain amount oftwist (hysteresis) is required to overcome the internal friction andcause the layers to come into interference with one another before therotary motion is observed at the output end. If the shaft is thentwisted in the alternate direction, the previous hysteresis must firstbe overcome to return the internal state of the wires to its staticcondition; then, a similar amount of hysteresis is introduced as theshaft is “wound up” in the new direction. This hysteresis is made worsewhen the flexible shaft traverses a curved path, because additionalstresses between the layers (resulting in increased internal friction)are introduced by the bending of the shaft through a curved path.

The previously described hysteresis in a pre-formed multifilar flexibleshaft prevents it from working as a precise transmitter of rotary motionfrom one end to the other. While these shafts may work well enough inthe unidirectional transmission of power, they are ineffective inprecisely transmitting a rotary control (in two rotational directions)because of the hysteresis or “lost motion” caused by their internalfriction.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a flexible rotaryshaft which has reduced hysteresis.

It is also an object of the invention to provide a flexible rotary shaftwhich has increased torque transmission.

It is another object of the invention to provide a multifilar flexiblerotary shaft which has little or no internal friction.

It is still another object of the invention to provide a flexible rotaryshaft which has accurate torque transmission when reversing from onerotational direction to the opposite rotational direction.

It is a further object of the invention to combine the benefits of amonofilar flexible rotary shaft with the benefits of a multifilarflexible rotary shaft while avoiding the deficiencies of each.

In accord with these objects which will be discussed in detail below,the multifilar flexible rotary shaft of the present invention includes aplurality of individual filaments which are not wound around each otheror around a central core. The input ends of each filament are coupled toeach other and the output ends of each filament are coupled to eachother. Preferably all of the filaments are identical and, for aplurality of N wires, each wire has 1/N the yield stress required totransmit the maximum torque required. While intuitively it seems thatthe filaments must be twisted together in order to transmit torque, suchis not the case. In fact, a group of N filaments can transmit N timesthe torque that can be transmitted by a single filament (up to its yieldstress) even if the wires do not touch one another. Thus, a looseensemble of N filaments can transmit N times the torque of a singlefilament, and will have N times the torsional stiffness of a singlefilament, while retaining the minimum radius of operation of a singlefilament. Since a loose ensemble of filaments would not have anyappreciable contact forces among the filaments (because they are notforcibly twisted together), there is no appreciable internal friction orhysteresis. In fact, in order to appreciably eliminate all thehysteresis in such an ensemble of filaments, the filaments should be nomore than loosely twisted together, if at all. In fact, the only reasonfor loosely twisting the wires together is to allow the ensemble to beeasily handled and to insure that the individual wire filaments followthe same general curved path from one end to the other. However, if therotary shaft is fabricated to a predetermined length and placed inside aflexible conduit, the filaments may be left completely loose, e.g. laidtogether in parallel.

The present invention describes a way of constructing a flexible shaftwith little or no internal friction. Such a flexible shaft will transmitrotary motion with little or no hysteresis, resulting in a precisetransmission of motion from one end to the other, even in cases ofreversing rotary motion, and while bent around small radii. In fact, theflexible shaft of the invention can be bent around radii as small ascould be negotiated by a monofilar flexible shaft having a diameterequal to the diameter of a single one of the individual filaments.

The invention has many practical applications, particularly in themanufacture of minimally invasive surgical instruments which musttraverse a tortuous path. Two particular examples are illustratedherein, i.e. a polypectomy snare instrument and a steerable flexiblemicrosurgical instrument with a rotatable clevis.

Additional objects and advantages of the invention will become apparentto those skilled in the art upon reference to the detailed descriptiontaken in conjunction with the provided figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of a prior art multifilarflexible rotary shaft;

FIG. 2 is a schematic side elevational view of the prior art multifilarflexible rotary shaft of FIG. 1;

FIG. 3 is a schematic, partially transparent, broken pseudo-perspectiveview of a multifilar flexible rotary shaft according to the invention;

FIG. 4 is broken side elevation in section of a snare instrumentutilizing a multifilar flexible rotary shaft according to the invention;

FIG. 5 is an enlarged cross-section taken through line 5—5 in FIG. 4;

FIG. 6 is an enlarged cross-section taken through line 6—6 in FIG. 4;

FIG. 7 is an enlarged cross-section taken through line 7—7 in FIG. 4;and

FIG. 8 is a side elevation view in partial longitudinal section of amicrosurgical cutting instrument utilizing a multifilar flexible rotaryshaft according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 3, a multifilar flexible rotary shaft 100according to the present invention includes a plurality of individualfilaments, e.g. 102, 104, 106, 108, 110, 112, 114. Each filament has aninput end, designated generally as “I” in FIG. 3 and an output end,designated generally as “O” in FIG. 3. All of the input ends are coupledto each other, for example by a coupling 116. All of the output ends arecoupled to each other, for example by a coupling 118. The filaments arenot tightly wound around each other or around a central core. However,they may be wound together loosely merely to facilitate handling of theshaft. Preferably all of the filaments are identical and, for aplurality of N wires, each wire has 1/N the yield stress required totransmit the maximum torque required for the shaft.

Discussion of Physical Principals of the Invention

If a torque is applied to a free mechanical body, that body will beginto take on an accelerating angular velocity. In order for the body toremain unaccelerated it is necessary for another torque, equal andopposite to the first torque, to be applied to it. It is not necessarythat the two equal and opposite torques be applied at the same point onthe body. Thus, rigid mechanical bodies effectively “add” or integrateall torques applied to them, and if the body is static (or rotating at aconstant angular velocity), it is an unavoidable conclusion that all thetorques applied to it sum to zero.

With this in mind, if two rigid free bodies are connected by a single,unsupported, monofilar wire filament, when the first body is rotatedwhile the second body is held fixed, the wire filament is torsionallydeformed, resulting in a “reaction torque” at the anchoring point of thesecond rigid body. Since the wire filament is unsupported, there are nosurface contact pressures on it, and hence no frictions resisting itsmotion or creating any reaction torque in the wire itself. The result isthat the reaction torque at the second body is equal in magnitude to theapplied torque on the first body. As long as the torsional stresses inthe wire filament are below the yield stress of the wire, this systemwill precisely transmit torque and rotary motion from one end to theother with no hysteresis. This construction is simple and intuitive.

It has been discovered that if a second unsupported monofilar wirefilament is coupled between the bodies, each wire acts independently:when the first body is rotated and the second body is held fixed,torques are applied to each of the wires independently. If the wires arethe same material, size, and length (and hence, the same torsionalstiffness), then the torque on each wire will be half the torque appliedto the first body. At the second body, each wire imparts its torque tothat body, so that the total torque applied by the two wires to thesecond body is the same as the torque applied to the first body. Thisanalysis is true if the wires are unsupported and no other forces areacted on them, even if the wires do not touch one another.

While intuitively one assumes that the wires must be twisted together inorder to transmit torque, such is not the case. In fact, a group of Nwires can transmit N times the torque that can be transmitted by asingle wire (up to its yield stress) even if the wires do not touch oneanother. Thus, a “loose ensemble of N wires” can transmit N times thetorque of a single wire, and will have N times the torsional stiffnessof a single wire, while retaining the minimum bend radius of a singlewire. Since a loose ensemble of wires does not have any appreciablecontact forces among the wires (because they are not forcibly twistedtogether), there is no appreciable internal friction or hysteresis. Infact, in order to appreciably eliminate all the hysteresis in such anensemble of wires, the wires should not be twisted together at all or atmost only loosely twisted together. In fact, the only reason for looselytwisting the wires together is to allow the ensemble to be easilyhandled and to insure that the individual wire filaments follow the samegeneral curved path from one end to the other.

In a practical construction of a shaft according to the inventiondescribed in detail below with reference to FIGS. 4-8, a group (e.g. 3or 4) of several small diameter (e.g. 0.005″ to 0.040″) wires are joinedat the first end, loosely arranged together (either parallel, looselytwisted, or braided), and then joined at the second end. The junctionsat the first and second end of the ensemble serve the functions of thefirst and second rigid bodies described in the analysis above. If thereare N wires in the ensemble, they will have N times the torsionalstiffness of a single such wire, and they will be capable oftransmitting N times the torque of a single such wire with noappreciable hysteresis. It should be noted that although a looseensemble of wires makes a very precise transmitter of rotary motion andtorque for small torques, it is not generally capable of transmitting aslarge a torque as a tightly-twisted strand of an equal number of similarwires because there is no way to resolve the torque applied to the firstbody into tensile stresses and compressive stresses in the wire bundleunless the wires are tightly twisted together so that they interferewith one another. As described below, the practical exemplaryembodiments are designed to transmit torques on the order of 0.1ounce-inch with an operational radius of approximately 0.8 inches.

It should also be noted that there is another advantage to a looseensemble of wires for transmitting rotary motion or torque around sharpbends. When a tightly twisted strand of wires is used as a flexibleshaft, it is usually enclosed inside a tubular sheath to contain thewires and reduce friction. When the sheath is bent around a tightradius, the outer layer of wires must slide along the internal surfaceof the sheath as the flexible shaft rotates. For a first-orderapproximation, the contact forces F_(contact) inside the sheath areequal to the stiffness of the tightly wound flexible shaftS_(flex shaft) divided by the radius of curvature R_(curve) of theshaft. The reactive torque T_(r (flex shaft)) created by this contactforce is equal to the product of the contact force F_(contact) times thecoefficient of friction C_(f) times the radius of the flexible shaftR_(s (flex shaft)). Thus, the reaction torque T_(r) of the tightly woundshaft is defined by:

T _(r (flex shaft))=(S _(flex shaft) /R _(curve))*C _(f) *R_(flex shaft)  (1)

However, in a loose ensemble of wires, when the ensemble is bent arounda curve, the wires each assume the maximum possible bend radius; thatis, they lay alongside each other on the inside of the sheath. For smallamounts of rotation, these individual wires will revolve independentlyabout their own axes rather than whirling around as a group; so, thereactive torque acting on each of them resulting from friction againstthe sheath would be:

T _(r (wire))=(S _(wire) /R _(curve))*C _(f) *R _(wire)  (2)

where S_(wire) is the stiffness of the wire and R_(wire) is the radiusof the wire. So, for an ensemble of N wires, the total reaction torqueon the ensemble is equal to:

T _(r (ensemble)) =N*(S _(wire) /R _(curve))*C _(f) *R _(wire)  (3)

Thus, the ratio of friction torque for the ensemble and the flexibleshaft would be:

 T _(r (flex shaft)) /T _(r (ensemble)) =[S _(flex shaft)/(N*S _(wire)]*[R _(flex shaft) /R _(wire)]  (4)

For an ensemble and a flexible shaft with the same torsionalstiffnesses, the flexural stiffness will also be equal, because thetorsional stiffness follows the same formula as the bending stiffness.Thus, the first term on the right side of equation (4) reduces toapproximately 1. The result is that the ratio of the friction torques(T_(r (flex shaft))/T_(r (ensemble))) is equal to the ratio of theradius of the flexible shaft to the radius of the individual wires inthe ensemble. So, the torque due to friction of a loose ensemble ofwires acting as a torque transmitter is smaller than the torque due tothe friction of a similarly stiff flexible shaft by the ratio of thediameters. For a typical assembly of seven wires, the ratio of diametersof the twisted flexible shaft to that of the individual wires is aboutthree to one, so the loose ensemble would have about one third thefriction in a similarly curved sheath. This result is valid for thecomparison of two very similar bundles of seven wires: one twistedtightly to form a flexible shaft and one loosely assembled into anensemble. (Note that this analysis assumes the stiffness of the flexibleshaft is equal to the sum of the stiffnesses of its individual wires,which is a very conservative assumption.)

From the foregoing analyses it is seen that there are three non-obviousadvantages to using a loosely-twisted (or non-twisted) ensemble of wiresas a torque-transmitting shaft versus using a similar tightly-twistedbundle of wires forming a traditional flexible shaft. First, there isgreatly reduced hysteresis in a loose ensemble versus a tightly-twistedflexible shaft. Second, the friction (for small angles of rotation) of aloose ensemble in a sheath is a fraction of the friction of anequivalent tightly-twisted flexible shaft. Third, the loose ensemble canwrap around a smaller radius than the tightly-twisted bundle.

The multifilar flexible rotary shaft of the invention has practical usein many different applications.

Description of Practical Applications Utilizing the Invention

One practical application for the invention is in the snare instrumentof the previously incorporated co-owned application. Turning now toFIGS. 4-7, a surgical snare instrument 210 includes an elongate flexibletubular sheath 212 having a proximal end 214 and a distal end 216, aflexible rotatable shaft 218 having a proximal end 220 and a distal end222 extending through and axially movable relative to the sheath 212, asnare 224 coupled to or formed at the distal end 222 of the shaft 218,preferably adjacent the distal end 216 of the sheath 212, and first andsecond handle assemblies 226, 228, respectively, for moving the shaft218 relative to the sheath 212.

The rotatable shaft 218 is preferably made from three high strength,straightened (camber-free) stainless steel wires of high elastic limit,each being approximately 0.012″ diameter. The proximal ends of the wiresare welded to each other and the distal ends of the wires are welded toeach other. Between their proximal and distal ends, the wires areloosely associated. The shaft 218 is adapted to be bent through atortuous path (e.g. through a radius of approximately 0.8 inches)without permanent deformation. In addition, for the reasons describedabove, it is possible to precisely rotate the snare 224 by rotating theshaft 218 at any point along its length.

The physician's handle assembly 226, which is the more distal of the twohandles, generally includes a body 230 and a knob 232 mounted in thebody 230 on bearings 233 a, 233 b in a manner which permits the knob 232to rotate coaxially relative to the body. The body 230 includes acentral bore 234 with one or more apertures 235, a threaded distal end236, and a threaded proximal end 238. The sheath 212 of the snareinstrument 210 is connected to the threaded distal end 236 of the body232, e.g., by means of a flare-nut connection 242. Preferably, astiffening sleeve 244 is provided over the sheath 212 at the connection242. The knob 232 includes a non-circular bore 240, e.g., having thecross-sectional shape of a square. The knob 232 (for reasons discussedbelow) is preferably at least as long as the distance of movementrequired to open and close the snare 224; i.e., the length of the snarewhen compressed in the sheath 212. The apertures 235 provide access tothe knob 232, so that the knob 232 can be rotated relative to the body230, e.g., by a physician.

A portion of the shaft 218 (preferably the proximal ends of the wireswhich are bound to each other) extending through the bore 240 of theknob 232 is provided with a key 246; that is, a spline element fixed onand about the shaft 218 or, alternatively, rigidly and fixedlyinterposed between two portions of the shaft. The key 246 preferably hasa rectangular shape but may have another non-circular shape. The key 246is slidably axially movable within the bore 240. Therefore, the shaft218 may be moved axially through the bore 240 (and that is why thelength of the knob 232 is preferably at least as long as the distance ofmovement required to open and close the snare). However, when the knob232 is rotated relative to the body 230, the key 246 within the bore 240is rotated and, consequently, the shaft 218 and snare 224 are rotatedrelative to the sheath 212.

The distal handle assembly 226 is preferably positioned approximately210 cm from the distal end 216 of the sheath 212 for a snare instrument210 designed to be inserted into a 200 cm endoscope. Thus, the physiciancan grip the body 230 in a manner which permits rotating the knob 232relative to the body, and hence the snare 224 relative to the sheath212, while using the body 230 as a grip to axially position the snareinstrument 210 within the working channel of an endoscope.

The shaft 218 extends out of the proximal end 238 of the body 320 to theproximal handle assembly 228, or assistant handle. The proximal handleassembly 228 preferably includes a stationary member 250 and a spoolmember 252 slidable relative to the stationary member. The stationarymember 250 includes a longitudinal throughbore 256 through which theproximal end 220 of the shaft 218 extends, a transverse slot 258, aproximal thumb ring 260, and a distal threaded connector 262. Theproximal end of the shaft 218 is preferably provided with a conductivestiffening sleeve 264, and a cylindrical conductive bearing 266 iscoupled about the proximal end of the stiffening sleeve 264. The spoolmember 262 includes a cross bar 68 which extends through the transverseslot 258 to secure the spool member 252 on the stationary member 250. Inaddition, the spool member 262 preferably includes a cautery plug 270.The conductive bearing 266 extends through the cross bar 268 and acollar 274 secures the bearing 266 in the cross bar 268 in a mannerwhich permits the conductive bearing to freely rotate within the crossbar 268. A spring 272 extends between the cautery plug 270 and theconductive bearing 266, and provides a contact between the plug 270 andthe bearing 266 regardless of the rotational position of the bearing266. Movement of the spool member 252 relative to the stationary member250 causes the snare 224 to extend from and retract into the distal end216 of the sheath 212. Those skilled in the art will appreciate thatsince the portion of the shaft between the proximal and distal handlesis not likely to traverse a tortuous path (between the physician and theassistant) it may be made of a monofilar wire or some other flexibleshaft which is not as flexible as that in the portion distal to thedistal handle.

As described in the previously incorporated application, an electricallyinsulative extension sheath 280 extends over the shaft 218 between theproximal end 238 of the body 230 and the distal end 262 of thestationary member 250, coupled, e.g., via flare-nut connections 282,284. Thus, there is a continuous outer connection joining, yet spacingapart, the distal handle assembly 226 and the proximal handle assembly228. A stiffening sleeve 286 is preferably provided over the extensionsheath 280 at the proximal end 238 of the body 230, and anotherstiffening sleeve 288 is preferably provided over the extension sheath280 at the distal end 262 of the stationary member 250.

In use, the physician introduces the snare instrument 210 into theendoscope (not shown), typically by means of a port in the endoscopehandle which communicates with the working channel of the endoscope.Then, the physician gives the proximal assistant's handle 228 to theassistant. The physician then grips the body 230 of the distalphysician's handle 226 of the snare instrument and uses it to positionthe distal end 216 of the sheath 212 adjacent to the polyp to beexcised. The physician then instructs the assistant to extend the snare,which is performed by moving the spool member 252 relative to thestationary member 250. The physician then uses the distal handle 226 tosimultaneously axially position and rotate the snare over the polyp byrotating the shaft 218 via the knob 232. Then, the physician instructsthe assistant to close the snare and sever the polyp, using cautery ifdesired. In this manner, the physician controls the means of positioningthe snare onto the polyp, and the assistant controls the opening andclosing of the snare and the cauterization.

Another practical application for the invention is in the microsurgicalcutting instruments disclosed in U.S. Pat. No. 5,439,478, the completedisclosure of which is hereby incorporated by reference herein.

Referring now to FIG. 8, a microsurgical instrument 380 incorporatingthe invention includes a flexible coil 314, a flexible rotatable shaft316 extending through the coil 314, distal end effectors 318 coupled tothe shaft 316, a rotatable clevis assembly 320 which is coupled to thedistal end of the coil 314, and a proximal actuation assembly 382. Theproximal actuation assembly 382 has a stationary handle portion 384which is provided with finger recesses 386, two of which are covered bya finger ring 385, and a throughbore 388 for receiving the coil 314 andflexible rotatable shaft 316. A lever arm 390 having a thumb ring 392 ispivotally attached to the stationary handle 384 by a pivot axle 394. Thelever arm 390 has a bore 396 which is substantially coaxial with thebore 388 in the stationary handle and a slot 398 which is substantiallyorthogonal to the bore 396. The slot 398 is fitted with a knurled disk400 having a shaft receiving bore 402 and a set screw 404.

The proximal end of the coil 314 is mounted within the throughbore 388of the stationary handle 384 by crimping, soldering, pressure fit orother suitable method. The proximal end of the flexible rotatable shaft316 is inserted into the bore 402 of the disk 400 and held in place bythe set screw 404. Those skilled in the art will appreciate that theshaft 316 is therefore rotatable relative to the actuation assembly 382by rotation of the knurled disk 400 inside the slot 398 in the lever arm390. It will also be appreciated that movement of the lever arm 390relative to the stationary handle 384 will cause a translationalmovement of the shaft 316 relative to the coil to open and close the endeffectors 318.

According to the invention, the flexible rotatable shaft 316 is madefrom three stainless steel wires, each having a diameter of 0.012inches. The proximal ends of the wires are welded to each other at theshaft receiving bore 402 and the distal ends of the wires are welded toeach other at the end effectors 318. Between their proximal and distalends, the wires are not tightly wound together, and are preferably notwound together at all. The typical length of the shaft 316 isapproximately 100-250 cm. The shaft will accurately transmit a torque ofapproximately 0.03 ounce-inches. The shaft 316 is capable of traversinga bend having a radius of 0.08 inches.

In operation, the practitioner holds the actuation assembly 382 withfingers wrapped around the recesses 386 and with the thumb inserted inthe thumb ring 392. The index finger is free to rotate the disk 400which effects a rotation of the shaft 316 and thus a rotation of theclevis 340 and end effectors 318.

Those skilled in the art will appreciate that the present invention isadvantageously used in conjunction with the other embodiments disclosedin the previously incorporated patents. Moreover, the invention isadvantageously used in conjunction with other steerable surgicalinstruments including forceps, baskets, ablators, crushers and drillers.The invention is also advantageously used in conjunction withcardiovascular instruments including blood pumping instruments whichutilize a flexible rotatable shaft, steerable forceps, rotary catheters,steerable electrodes, steerable injection needles, and steerable cauterydevices. In addition to various endoscopic instruments, the invention isadvantageously utilized in conjunction with various laparoscopicinstruments such as: catheters for cannulating the fallopiantubes/uterus, steerable scissors, graspers, dissectors and cauteryprobes, resection devices, and ablation devices. The invention is alsoadvantageously used in other steerable devices such as guidewires. Inaddition to surgical devices, the invention finds useful application insuch unrelated arts as miniature flexible shafts for control or powertransmission, aircraft control cables, remote instruments such ascompasses and wind direction instruments, dental drills, speedometerdrive cables, and steerable inspection scopes.

There have been described and illustrated herein several examples of amultifilar flexible rotary shaft. While particular embodiments andapplications of the invention have been described, it is not intendedthat the invention be limited thereto, as it is intended that theinvention be as broad in scope as the art will allow and that thespecification be read likewise. Thus, while particular dimensions havebeen disclosed, it will be appreciated that other dimensions could beutilized. Also, while a particular number of filaments have been shown,it will be recognized that the number of filaments will be determined bythe application. Moreover, while particular configurations have beendisclosed in reference to welding the ends of the filaments, it will beappreciated that other means for binding the ends together could be usedas well. It will therefore be appreciated by those skilled in the artthat yet other modifications could be made to the provided inventionwithout deviating from its spirit and scope as so claimed.

What is claimed is:
 1. A medical device, comprising: a flexible sheath having a proximal end and a distal end; a shaft having a proximal end and a distal end, the shaft comprised of a plurality of individual wires each having a proximal end and a distal end; wherein the shaft is slidably and rotatably disposed within the sheath; and wherein the proximal end of each individual wire filament is coupled to the proximal end of each other individual wire filament, the distal end of each individual wire filament is coupled to the distal end of each other individual wire filament, and substantially the entire length between their proximal ends and their distal ends the individual wire filaments are loosely associated.
 2. The medical device of claim 1, further comprising an end effector coupled to the distal end of the shaft.
 3. The medical device of claim 2, wherein the end effector includes a snare.
 4. The medical device of claim 1, further comprising a first handle that includes a rotating member for rotating the shaft relative to the sheath.
 5. The medical device of claim 4, wherein the first handle further comprises a sliding member for longitudinally sliding the shaft relative to the sheath.
 6. The medical device of claim 4, further comprising a second handle including a sliding member for longitudinally sliding the shaft relative to the sheath.
 7. The medical device of claim 1, wherein the sheath is adapted and configured for being disposed within a channel within an endoscope.
 8. The medical device of claim 1, wherein the individual wire filaments are arranged generally parallel to one another.
 9. The medical device of claim 1, wherein the individual wire filaments are loosely twisted about one another.
 10. The medical device of claim 1, wherein the individual wire filaments are loosely braided.
 11. A medical device, comprising: a flexible sheath having a proximal end and a distal end; a shaft having a proximal end and a distal end, the shaft comprised of a plurality of individual wires each having a proximal end and a distal end; wherein the shaft is slidably and rotatably disposed within the sheath; and wherein the proximal end of each individual wire filament is coupled to the proximal end of each other individual wire filament, the distal end of each individual wire filament is coupled to the distal end of each other individual wire filament, and between their proximal ends and their distal ends the individual wire filaments are loosely associated; further comprising an end effector coupled to the distal end of the shaft; and wherein the end effector includes a clevis assembly.
 12. A medical device, comprising: a flexible sheath having a proximal end and a distal end; a shaft having a proximal end and a distal end, the shaft comprised of a plurality of individual wires; wherein the shaft is slidably and rotatably disposed within the sheath; and wherein the individual wires are loosely associated with one another along substantially the entire length between the proximal end and the distal end of the shaft.
 13. The medical device of claim 12, further comprising an end effector coupled to the distal end of the shaft.
 14. The medical device of claim 13, wherein the end effector includes a snare.
 15. The medical device of claim 12, further a first handle that includes a rotating member for rotating the shaft relative to the sheath.
 16. The medical device of claim 15, wherein the first handle further comprises a sliding member for longitudinally sliding the shaft relative to the sheath.
 17. The medical device of claim 15, further comprising a second handle including a sliding member for longitudinally sliding the shaft relative to the sheath.
 18. The medical device of claim 12, wherein the sheath is adapted and configured for being disposed within a channel within an endoscope.
 19. The medical device of claim 12, wherein the individual wire filaments are arranged generally parallel to one another.
 20. The medical device of claim 12, wherein the individual wire filaments are loosely twisted about one another.
 21. The medical device of claim 12, wherein the individual wire filaments are loosely braided.
 22. A medical device, comprising: a flexible sheath having a proximal end and a distal end; a shaft having a proximal end and a distal end, the shaft comprised of a plurality of individual wires; wherein the shaft is slidably and rotatably disposed within the sheath; and wherein at least a portion of the individual wires are loosely associated with one another substantially the entire length between the proximal end and the distal end of the shaft; further comprising an end effector coupled to the distal end of the shaft; and wherein the end effector includes a clevis assembly.
 23. A medical device, comprising: a sheath having a proximal end and a distal end; a shaft having a proximal end and a distal end, the shaft comprised of a plurality of individual wires; wherein the shaft is movable within the sheath; and wherein the individual wires are loosely associated with one another along substantially the entire length between the proximal end and the distal end of the shaft. 